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    IR laser line scanning treatments to improve levitation forces in MgTi0.06B2 bulk materials
    (Elsevier Science Sa, 2019) Ozturk, K.; Aksoy, C.; Angurel, L. A.; Savaskan, B.; Martinez, E.; Badia-Majos, A.; de la Fuente, G. F.
    Infrared (IR) laser-line scanning has been widely used to induce different surface microstructures in a broad range of materials. In this work, this laser configuration was applied on the surface of MgTi0.06B2 bulk samples in order to ascertain its effects on their superconducting properties, particularly on the magnetic levitation forces. The microstructural changes produced by this type of laser treatment were investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). It was observed that the thermal treatment induced by the laser improves grain connectivity in a layer of material just below the irradiated surface, in agreement with the observed improvement in critical current density values, J(c), which were estimated from isothermal magnetic hysteresis loops. A significant increment of both vertical (F-z) and lateral (F-x) magnetic levitation forces was achieved. Numerical calculations were performed to understand the experimental behaviour and to clarify how an improvement of J(c) near the surface can improve the magnetic levitation force of these materials. In addition, the same studies were carried out in similar bulk samples but with nano-sized silver particle additions of 3 and 6 wt %, in the outer ring of the bulk, observing also an improvement of the levitation forces, albeit less than in samples without Ag because of the better performance of the original samples after laser treatment. These results are relevant to those studying superconductor fabrication and material fabrication modelling, essential for the development of technological applications of superconductors, and are based on microstructure control via application of a recently developed laser-line scan method. (C) 2019 Elsevier B.V. All rights reserved.
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    The investigation on the regional nanoparticle Ag doping into MgTi0.06B2 bulk for improvement the magnetic levitation force and the bulk critical current
    (Elsevier Science Sa, 2017) Ozturk, K.; Dancer, C. E. J.; Savaskan, B.; Aksoy, C.; Guner, B.; Badica, P.; Aldica, G.
    Fabrication methods are important way to improve structural and superconducting properties of MgB2 such as critical current, magnetic levitation force (MLF) and magnetic field trapping capability. Although the graded fabrication technique has been used for single-grain bulk YBCO superconductor to improve critical current and bulk superconducting properties, similar technique as regional doping has not been used for bulk MgB2, until now. In this study, nanoparticle silver doping was carried out in to the bulk MgTi0.06B2 superconductor by using in-situ solid state reaction and partial graded (regional) doping method together, to improve the radius independent uniform bulk current density and the magnetic levitation force as well as the structural properties of the MgB2 bulk superconductors. Both the J(c)(0) self-field critical current and F-p (mu H-0) pinning force density values enhanced in comparison with the inner region values, when the nanoparticle Ag doping is carried out in to the outer section of the sample. Addition to the enhancement of the structural and the micro electromagnetic properties as J(c)(0) and Fp (mu H-0), our study also focused on the improved of the bulk Jc and the radius of shielding current loop r, to improve bulk electromagnetic properties as the levitation force. It is seen that the structural properties enhanced and both the vertical levitation force and the lateral guidance force value increased with Ag doping to the outer section of MgTi0.06B2 sample. On the other hand, the increasing ratio of the lateral guidance force of 19.7% and the vertical levitation force of 10.8% of the sample with 3 wt% Ag-doped than the undoped one points out that the regional doping method to the outer section is very suitable for guidance force applications, which is important in the magnetic bearing application such as Maglev and magnetic energy storage systems. (C) 2017 Elsevier B.V. All rights reserved.